Question: Captain Cox, among the most nerve-wracking periods when flying is descending through a layer of storm clouds when visibility is zero and the aircraft is being buffeted. Please describe the pilot's actions and mental state during this period.

- Submitted by reader Edward Robinson, Savannah, Ga.

Answer: During a descent in instrument conditions, when there is no visibility of the ground, pilots are flying according to a predefined path to align them with the runway. Usually air traffic control will provide guidance of the heading to fly until receiving radio signals to align with the runway. This is a normal process for pilots, and while it is busy, it is a routine part of the flight. Professional pilots are equally comfortable flying under instrument rules as they are flying visually.

Q: Captain, I recently had a long flight delay out of Boston Logan due to fog. Arriving planes were being diverted, I would guess due to visibility. Why can an ILS approach not be used in this situation?

- Jeff, Boston

A: Boston has very good ILSs (instrument landing systems), however they have visibility requirements. If the fog was too thick, causing the visibility to be below landing limits, then a diversion is necessary.

Runway 4R at Boston Logan has a CAT III ILS which allows for very low visibility requirements. It is very unusual for a CAT III runway to go below limits, however not all airplanes are capable of CAT III approaches.

Q: Which is the most unfavorable weather for you to fly the plane?

- Sam Singh, USA

A: The most challenging weather to me were blizzards with high winds, low visibility, and ice-covered runways (and taxiways).

John Cox is a retired airline captain with U.S. Airways and runs his own aviation safety consulting company, Safety Operating Systems.